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Re: Check that unlinked uses do not contain ssa-names when renaming.

On 08/10/12 11:24, Richard Guenther wrote:
> On Sun, Oct 7, 2012 at 12:44 PM, Tom de Vries <> wrote:
>> Richard,
>> attached patch checks that unlinked uses do not contain ssa-names when renaming.
>> This assert triggers when compiling (without the fix) the PR54735 example.
>> AFAIU, it was due to chance that we caught the PR54735 bug by hitting the
>> verification failure, because the new vdef introduced by renaming happened to be
>> the same name as the ssa name referenced in the invalid unlinked use (in terms
>> of maybe_replace_use: rdef == use).
>> The assert from this patch catches all cases that an unlinked use contains an
>> ssa-name.
>> Bootstrapped and reg-tested on x86_64 (Ada inclusive).
>> OK for trunk?
> I don't think that is exactly what we should assert here ... (I thought about
> adding checking myself ...).  What we'd want to assert is that before
> any new DEF is registered (which may re-allocate an SSA name) that
> no uses with SSA_NAME_IN_FREELIST appear.  Thus, a light verification
> pass would be necessary at the beginning of update_ssa
> (which I queued onto my TODO list ...).  We'd want that anyway to for
> example catch the case where a non-virtual operand is partially renamed.


while developing a patch, I ran into the same 'no immediate_use list'
verification error again, caused by an unlinked use containing an ssa-name.

The verification error was caused by an error in my patch, but triggered by
chance, by an unrelated change in the patch.

I've tried to implement the 'light verification pass' you describe above, and
I've checked that the error in my patch is found, also when I remove the trigger
for the verification error from my patch.

Bootstrapped and reg-tested on x86_64 (with the ENABLE_CHECKING guarding
removed, in order to ensure the code is active).

OK for trunk?

- Tom

2014-10-16  Tom de Vries  <>

	* tree-into-ssa.c (update_ssa): Assert that there's no ssa use operand

diff --git a/gcc/tree-into-ssa.c b/gcc/tree-into-ssa.c
index 01203de..227d5bb 100644
--- a/gcc/tree-into-ssa.c
+++ b/gcc/tree-into-ssa.c
update_ssa (unsigned update_flags)
   timevar_push (TV_TREE_SSA_INCREMENTAL);
+  FOR_EACH_BB_FN (bb, cfun)
+    {
+      gimple_stmt_iterator gsi;
+      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+	{
+	  gimple stmt = gsi_stmt (gsi);
+	  ssa_op_iter i;
+	  use_operand_p use_p;
+	    {
+	      tree use = USE_FROM_PTR (use_p);
+	      if (TREE_CODE (use) != SSA_NAME)
+		continue;
+	      gcc_assert (!SSA_NAME_IN_FREE_LIST (use));
+	    }
+	}
+    }
   if (dump_file && (dump_flags & TDF_DETAILS))
     fprintf (dump_file, "\nUpdating SSA:\n");

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